The principal objective of this proposal is to study some of the biochemical processes that underlie differentiation; particular emphasis will be placed on the involvement of plasma membrane and ornithine decarboxylase (ODC). Mouse neuroblastoma cells can be induced to differentiate by cAMP. The differentiated cells lose their tumorigenicity. Increased tyrosine hydroxylase (TH) activity and neurite outgrowth are two distinct phenotypic expressions of differentiation in neuroblastoma cells. The possible involvement of membrane protein phosphorylation in mediating the effect of cAMP in cytodifferentiation will be studied. Differences in the composition of plasma membrane proteins of malignant and differentiated neuroblastoma cells will be probed by two surface labeling techniques (lactoperoxidase catalyzed iodination, and galactose oxidase catalyzed reductive tritiation), as well as by phosphorylation of purified membranes catalyzed by endogenous protein kinases. cAMP causes the induction of ODC and TH in neuroblastoma cells. These two enzymes are the rate-limiting enzymes in the synthesis of polyamines and catecholamines, respectively. The mechanism by which cAMP induces ODC, and the involvement of ODC in cytodifferentiation will be studied. The approach is to delineate the relationship between cAMP-induced membrane protein phsophorylation changes and the increase in ODC activity. The temporal and/or causal relationship between the cAMP-induced increase in ODC activity and TH activity will be investigated. The approach is to correlate changes of the two enzyme activities under conditions where ODC activity is varied. The proposed studies should help us to understand the role of cAMP and polyamines in cytodifferentiation. In addition, knowledge on the composition of plasma membranes of malignant vs. differentiated cells should help us to gain a better insight into the understanding of tumor reversion. Our long-term goal is to be able to design drugs which specifically modulate the various biochemical processes which underlie differentiation, so that differentiation and tumor reversion can be manipulated pharmacologically.